The present invention relates to a coupling made of synthetic resin used for piping system transferring poisonous fluid of high temperature and high pressure in a field of so-called high technology such as mainly semiconductor production, and method for manufacturing a pipe used for this coupling and its manufacturing apparatus.
As a coupling's mechanism of plastic pipe, various tight sealing structures using of a tight sealing taper screw and ferule and others are known.
However, for instance, in fluoric resins such as TFE(polytetrafluoroethylene), PFA(copolymer of polytetrafluoroethylene and perfluoroalkylvinylether), FEP(copolymer of polytetrafluoropropylene) and the like, in accordance with their characteristics, poisonous materials and the like of high temperature and high pressure are many in fluid used for that, and a leakage of fluid are produced which occurs by causes of repeating of expansion and contraction due to heat cycle and generation of creeping and the like.
This is because mainly fine gaps are produced causing from above factors to a joining portion, and a prevention for this is very difficult. Therefore, in conventional couplings and in those kinds, a using in condition at below about temperature of 120 degrees in Centigrade and pressure of 2 Kg/c of fluid is inevitably done.
In accordance with the coupling of the present invention, front end portion of resin pipe folded back and formed in U-shape is coupled to an inner annular portion of tightening means, a folded portion of the resin pipe- positioned at concave portion of inner annular portion, its U-shaped bottom is closely contacted and fixed by an end edge of the inner annular portion and a curved groove of stopper portion according to the screw-coupling of the tightening means and a coupling's main body, and a protruded strip band strengthens a close contact of coupling's main body inner surface and a concave outer circumferential surface of resin pipe folded back portion and at the same time, a lip seal makes a close contacting degree of inner surface of tile coupling main body and an inner circumferential surface of the inner annular portion to be firm and secure, so that a coupling for a pipe of resin of very high in reliability especially fluorine resin can be realized without producing any problem of leakage and the like even in allowable limit range further above the temperature condition and pressure condition of fluid in conventional coupling.
And yet, one which may be cited as a requisite condition for above described coupling is a structure which folded back a pipe opening end to outer side. However, to make a front end of fluorine resin pipe and the like to be simply, exactly and rapidly folded back with meeting to joining condition is very difficult.
Heretofore., although it might have been thought that to fold back a front end of resin pipe toward outside at normal temperature and the like was impossible, a technique for folding back an end portion of resin pipe was almost nothing.
Therefore, an inventor of this application has researched and developed a method for folding back an end of opening of resin pipe and apparatus used for this folding back method comprising a process for making an annular body to outer circumference of a pipe having a core material at inner hollow in compliance with requirement, and a process for continuing to press the pipe opening end to axial direction of the pipe with expanding to outward, and with outwardly expanding the front end by skillfully utilizing a characteristic, particularly elasticity of the resin and simultaneously folding back the pipe opening end naturally at certain time point, and inserting the pipe opening end folded back to outer circumference of aforesaid annular body, in a process of peripheral technique development of aforementioned joining structure.